Side-shift limiter

ABSTRACT

A side shift limiting attachment for a material handing vehicle alerts the vehicles operator and restricts side shifting, lifting, tilting and/or rotation of the attachment when the side shift displacement is approaching or has reached a limit for a lift height.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

BACKGROUND OF THE INVENTION

The present invention relates to a load engaging apparatus for use withmaterial handling equipment and, more particularly, to controls fortransversely movable load engaging members such as forks or clamp armsof a load engaging apparatus associated with material handlingequipment.

Material handling equipment used for moving palletized or non-palletizedloads from place to place, such as, for example, in a warehouse,typically includes forklift trucks or other types of material handlingequipment equipped with load engaging members such as forks or clamparms. For example, on a typical forklift truck load engaging forks areattached to a carriage which is in turn movably secured in a mast so asto enable the carriage and forks to travel vertically in the mast.Various types of attachments may also be mounted on the carriage orinclude an integrated with the carriage. For example, a sideshifterwhich moves the forks transversely in unison and/or a fork positionerwhich enables movement of the forks transversely toward and away fromeach other may be either attached to the carriage or integrated with thecarriage structure. Likewise, a load clamp having load-engaging clamparms similarly movable transversely either in unison either or toward orand away from each other may be attached to the carriage or integral tothe carriage. Some attachments also include amotor a motor enablingrotation of the load engaging members and thereby the load about an axissubstantially parallel to the longitudinal axis of the material handlingequipment.

Load clamps rely on clamping forces applied to the sides of the load forsecuring the load for lifting and clamp arms may be engineereddifferently for handling rectangular or cylindrical loads. For example,paper roll clamps and drum-clamping forks may incorporate contoursparticularly useful for clamping cylindrical loads. On the other hand,“carton clamps” generally refers to clamps with clamp arms adapted tohandle rectangular loads such as stacked cartons or householdappliances. Carton clamp attachments typically include a pair of largeblade-shaped clamp members each of which can be inserted betweenside-by-side stacks of cartons or appliances to bracket a loadcomprising one or more appliances or cartons. The clamp members oneither side of the load are then drawn together, typically, usinghydraulic cylinders to move the clamp members and to apply sufficientcompressive force to the load to allow it to be lifted. To securely holdthe load, the surfaces of the clamp members which contact the sides ofthe load are typically constructed of materials such as rubber facedaluminum providing a high coefficient of friction. Carton clamps aremost frequently used in the warehousing, beverage, appliance, andelectronics industries and may be specifically designed for particulartypes of loads. For example, carton clamps may be equipped with contactpads that are sized for palletless handling of refrigerators, washers,and other large household appliances (also referred to as “whitegoods”). In various configurations, carton clamps may be used forhandling multiple appliances at one time.

In addition to clamping a load in order to lift and move the load,clamps may be equipped with side-shifting capabilities whereby theclamped load may be repositioned from side-to-side with the clampingmembers moving transversely in one direction or the other in unison.Similarly, a fork positioner enabling transverse movement of loadsupporting forks to increase or decrease the distance between the forksmay also include side-shifting enabling transverse movement of the forksin unison. When the longitudinal axis of the material handling vehicleis not perfectly aligned, transversely, with the center of a load, astack or a rack space, side shifting can enable lateral alignment of theload engaging members, clamp arms or forks, with the load, stack or rackopening in which the load is to be engaged or deposited without furthermaneuvering of the vehicle. In addition, efficient utilization of space,notably when loading a transport vehicle, such as a trailer or railcar,commonly requires that loads be placed in close proximity to a wall oranother obstacle. Side shifting allows loads that are narrower than thematerial handling vehicle to be placed close to a wall without firstdepositing the load and then pushing it, potentially, damaging it or thematerial handling vehicle. The side-shifting function may be actuated byone or more hydraulic cylinders separate from the clamping/forkpositioning cylinder(s) (“external” side-shifting), or by theclamping/fork positioning cylinders themselves (“internal”side-shifting).

While side shifting is operationally advantageous, the off-centerposition of the load relative to the material handling vehicle adverselyimpacts the stability of the vehicle, particularly when the load iselevated. To compensate for the off-center weight of the load, amaterial handing vehicle may be “de-rated” and relegated to handlingloads that are lighter than the nominal capacity load for the samevehicle when it is not equipped for side shifting. Conversely, a highercapacity, more expensive and less maneuverable material handing vehiclemay be required to handle a load of a particular size or weight if theload can be side shifted.

What is desired, therefore, is a system and apparatus which optimizesthe capability of a material handling vehicle equipped for sideshifting.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an exemplary forklift truck equippedwith a load clamp.

FIG. 2 is a perspective view of a carton clamp attachment for a forklifttruck arranged for limited internal side shifting.

FIG. 3 is a schematic of a side shifting clamp attachment and a sideshift limiting system for a material handling vehicle.

FIG. 4 is a plan view of a forklift truck operating in a walled area.

FIG. 5 is a schematic representation of a forklift truck.

FIG. 6A is a first portion of a flow diagram for a method of side shiftlimiting.

FIG. 6B is a second portion of the flow diagram of FIG. 6A.

FIG. 7 is a graphic representation of side shift limits vs lift heightand back tilt for a forklift truck.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the preferredembodiments. However, those skilled in the art will understand that thepresent invention may be practiced without these specific details, thatthe present invention is not limited to the depicted embodiments, andthat the present invention may be practiced in a variety of alternateembodiments. In other instances, well known methods, procedures,components, and systems have not been described in detail.

Although the preferred embodiments may be implemented in a wide varietyof configurations involving different types of material handlingequipment and different types of attachments, the following detaileddescription, where comparable elements are referred to with likereference numbers, discloses the preferred embodiments principally inthe context of an exemplary forklift truck 100, as illustrated in FIG.1, fitted with a carton clamp attachment 102. As shown in FIGS. 1 and 2,the carton clamp attachment 102 is configured for handling white goodssuch as the four washers 106, 108, 110, 112 clamped between a firstclamping member 116 (sometimes referred to as a clamp arm having acontact or clamp pad, which is shown engaging two of the washers 106,110) and a second, oppositely oriented clamping member 118 which ishidden by the washers in the perspective view of FIG. 1. The cartonclamp attachment 102 may comprise a frame 104 that is attachable to acarriage movably secured in a mast assembly 114 mounted to the front ofthe forklift truck 100 or the attachment's frame may be movablysecurable in the forklift truck's mast and function as the carriage.Such carriage and mast assembly structures are well known and need notbe described in further detail.

Referring also to FIG. 3, the exemplary carton clamp attachment 102includes a pair of large blade-shaped clamp members 116, 118, shownschematically in FIG. 3 and shown structurally in FIG. 2, which can bepositioned on opposing sides of a stack of appliances such as thewashers 106, 108, 110, 112 as shown in FIG. 1. Preferably, the forkliftis moved forward until the load engages the attachment's load face 120,a portion of the attachment's structure, such as a portion of the frame104 or the vertical face of load supporting forks, which is engageablewith the load and which limits the load's displacement in the directionof the forklift. The clamp members on either side of the load (i.e. thewashers 106, 108, 110, 112) are drawn together or moved apart byhydraulic cylinder assemblies 122, 124 controlled byclamp-closing/opening hydraulic circuitry shown schematically in FIG. 3.The hydraulic cylinder assemblies apply a compressive force to the loadwith sufficient pressure to enable the clamp members to frictionallysecure the load for lifting.

Referring also to FIG. 4, the carton clamp attachment 102 is preferablyequipped with side-shifting capabilities whereby a datum 130, forexample, the center of the opening 133 between the load engagingmembers, for example, the clamp arms 116, 118, defining the lateralposition of the load face 120 may be repositioned laterally with respectto the frame 104 of the attachment 102 and, since the frame of theattachment is fixed laterally with respect to the forklift truck, alateral reference datum for the forklift truck such as the forklifttruck's longitudinal center line 134. The exemplary clamp 102 includesinternal side-shifting capabilities where the same hydraulic cylinders122, 124 are arranged to move in opposite directions for clamping andunclamping and to move in unison in the same direction for sideshifting. However, shift-shifting may also be of an external type usingseparate hydraulic cylinders for, respectively, clamping andside-shifting movements.

A forklift truck commonly must be turned at a right angle to the aislein which it is traveling to engage or deposit a load complicatingalignment of the load engaging members with a load to be engaged or alocation for depositing a load. If the longitudinal centerline 134 ofthe forklift is not aligned with the center of the load to be engaged orthe place where the load is to be deposited, for example, on a stack,considerable maneuvering may be necessary to move the forklift laterallyso that the load engaging members or the load is in the proper position.Side shifting promotes efficiency in forklift operation and reducesoperator stress by enabling limited lateral repositioning of the loadengaging members relative to the location where the load is to beengaged or deposited without maneuvering the forklift. This promotesmore stable stacking and reduces the potential for damage. Asillustrated in FIG. 4, side-shifting is also advantageous whendepositing a load which is narrower than the forklift proximate a wallor other obstacle, such as for example, when loading an intermodalcontainer or a transport vehicle 402, such as a highway trailer or arailcar. The ability to deposit a load close to a wall 404 is importantfor the full and efficient utilization of the available volume of thewalled area and sideshifting avoids the need to deposit the load andthen push it toward the wall which can result in damage to the loadand/or the forklift truck.

While side shifting is advantageous, the lateral displacement of theload relative to the forklift adversely impacts the stability of theforklift particularly when the load is elevated. Referring to FIG. 5,for visualizing the effect of side shifting on the stability of aforklift truck, a counterbalanced forklift may be represented as apyramid 502 with a triangular base 504 defined by a first axis 506, A-B,extending between the respective areas of contact of the forklift'sfront or load wheels 508, 510 and second 512 and third 514 axes, A-C andB-C, extending from the center pivot of the rear axle 516 to respectiveareas of contact of the load wheels. Gravity acts vertically at thecombined center of mass 520, which is concentrated at the apex of thepyramid and represents the center of mass 522 of the unladen forklift522 combined with the center of mass 524 of the load 524, if any. On theother hand, dynamic forces produced by changes in speed and/or directionof the forklift and the load act horizontally at the combined center ofmass to urge movement of the center of mass in the direction of at leastone of the axes defining the base of the pyramid, A-B, A-C, B-C. Forexample, braking while moving forward urges the combined center of masstoward axis A-B and centrifugal force produced by turning urges thecombined center of mass laterally toward one of the bounding axes A-C orB-C. The pyramid (the forklift) will tip if the combined center of massof the forklift moves outside of the triangular base 504.

If a capacity load is carried low and centered, the combined center ofmass 520 will be located closer to the axis A-B than the center of mass522 of the unladen forklift 522 and substantially distal of axes A-C andB-C. While resistance to tipping forward when braking is lower, theforklift has substantial reserve resistance to tipping to the sidebecause the low position of the combined center of mass 520 means thehorizontal forces are applied to a relatively short moment arm and mustdisplace the combined center of mass a substantial distance beforereaching either axis A-C or B-C. But when the load (center of mass 524)is raised toward point 524′, the combined center of mass 520′ rises withthe load to a location more distant from the three axes defining thebase of the pyramid, increasing the length of the lever arm on which thehorizontal forces act and lowering the resistance of the forklift totipping in all directions. And when the center of mass of the load ismoved laterally away from the longitudinal centerline 134 of theforklift toward point 524″, for example, by side shifting, the combinedcenter of mass moves in the direction that the load was shifted towardpoint 520″ and closer to one of the axes, A-C or B-C, reducing theresistance of the forklift to tipping to the side. Furthermore, tiltingthe mast back shifts the load toward point 524′″ and the combined centerof mass rearward toward point 520m 520′″ and the apex of the triangularbase and even closer to the axes A-C and B-C. Tilting is commonlylimited if a forklift is equipped with a mast capable of lifting tosubstantial heights and may also be restricted if the forklift isequipped for side shifting.

Forklift trucks equipped for side shifting are commonly “derated,” thatis, the maximum weight of the load that is to be handled with the sideshift-capable forklift truck is less than the rated load of the sameforklift when not equipped for side-shifting. Conversely, a larger, lessmaneuverable and more expensive forklift may be required to handle aparticular load when the forklift is equipped for side-shifting.However, the inventors herein have realized that the greatest lateralmovement of the load is often desired when the load is at a relativelylow lift height, for example, to place a load proximate a wall of atransport vehicle, and when the load is lifted higher, more limitedlateral shifting of the load will often suffice to permit centering theload engaging members with respect to a load or aligning a load with astack or a rack opening. In addition, restricting side shifting speed asthe lift height, back tilt and/or lateral displacement of the loadincreases reduces the dynamic forces resulting from acceleration anddeceleration of the load. The inventors have concluded that the capacityof a forklift truck can be optimized by limiting the lateraldisplacement and speed of the load when it is lifted to greater heightsand/or tilted rearward while allowing maximum side-shifting displacementand speed at lower lift heights.

Referring to FIG. 3, the exemplary forklift 100 is equipped with asystem 302 that limits the lateral speed and displacement of the sideshifting attachment 102 according to the lift height and, preferably,the back tilt of the mast and announces one or more alerts to theforklift's operator when lateral displacement of the attachment isapproaching or has reached one or more limits. The pair of hydrauliccylinder assemblies 122, 124 are arranged to move the load engagingmembers, clamp arms 116, 118, in directions transverse to thelongitudinal axis 134 of the forklift. The exemplary attachment 102 isarranged for internal side shifting with the hydraulic cylinderassemblies 122, 124 connectable to a source of pressurized fluid, pump304, in ways that cause the cylinders to either extend or retract inopposing directions to clamp or unclamp a load between the clamp arms116, 118 or to extend or retract in the same direction to move a loadface datum defining the lateral position of the attachment's load face,for example, the lateral centerline of the load face 130 defined by theclamp arms, relative to the lateral center 132 of the attachment's frame104 and thereby relative to a datum establishing the lateral position ofthe forklift 100, for example, the longitudinal centerline 134 of theforklift.

Typically, the pump 304 is driven by a motor or engine (not shown) ofthe material handling equipment, for example, the exemplary forklifttruck 100, and draws fluid from a reservoir 306 and discharges the fluidto a supply conduit 308. When the plural control valves 310, 312, 314,712 713 and 716 are centered (as pictured) and blocking the passage offluid toward the system's actuators, i.e. the hydraulic cylinderassemblies 122, 124 and the motor 315, passages in each of the controlvalves and an open center conduit 316 connect the supply conduit 308 tothe reservoir 306. If the pressure in the supply conduit 308 exceeds asystem relief pressure, a system relief valve 318 will permit fluid toflow from the supply conduit to the reservoir.

The exemplary system 302 includes a clamp/unclamp control valve 312 or,if the forklift truck is equipped with a fork positioner attachment, afork position control valve, which includes a valve spool that isshiftable to the left from the illustrated center position blocking flowto a second position enabling pressurized fluid to flow from the supplyconduit 308 and open center conduit 316 through conduits 320 and 352 tothe rod ends 322, 324 of the hydraulic cylinder assemblies 122, 124.Pressure in the rod ends 322, 324 urges the cylinders to retract movingthe clamp arms 116, 118 toward each other to clamp a load. Pressure inconduit 320 unseats a pair of pilot operated check valves 326, 328allowing fluid to flow out of the piston ends 330, 332 of the hydrauliccylinders through conduits 334, 336. The fluid expelled from the pistonends of the hydraulic cylinders 122, 124 flows through a flowdivider/combiner valve 338 which maintains a substantially equal flowfrom the piston ends of the respective cylinders so that the cylindersretract at substantially the same rate. The fluid from the piston ends330, 332 of the hydraulic cylinders 122, 124 flows from the flowdivider/combiner valve 338 to the reservoir 306 through a conduit 340, apassage in the clamp/unclamp control valve 312 and the open centerconduit 316. Conversely, shifting the clamp/unclamp control valve 312 tothe right from the center position directs pressurized fluid throughconduit 340 to the flow divider combiner valve 338 and then throughconduits 334, 336 and check valves 326, 328 to the piston ends 330, 332of the hydraulic cylinders 122, 124. Pressure in the piston ends of thehydraulic cylinders 122, 124 urges extension of the hydraulic cylindersand opening of the clamp arms 116, 118 and forces fluid from the rodends 322, 324 of the hydraulic cylinders back to the reservoir 306 viaconduits 320, 352 and the pilot operated check valve 350 which, due topressure in conduit 340, is open.

The side shift control valve 310 is also a three position valve with acenter position (as illustrated) blocking flow toward the hydrauliccylinders 122, 124. When the valve is moved to the left from theillustrated centered position, fluid is directed from the open centerconduit 316 to conduit 342 and a right secondary side shift controlvalve 346 which is normally open permitting flow into conduit 343 to thepiston end 332 of the right hand hydraulic cylinder 124. The pressure inthe piston end of the right-hand hydraulic cylinder 124 urges thecylinder to extend and move the right hand clamp arm 116 to the right.Fluid is forced out of the rod end 324 of the right hand cylinder 124but the check valve 350 blocks flow to the reservoir 306 forcing thefluid to flow to the rod end 322 of the left hand hydraulic cylinderassembly 122 through conduit 352. Fluid is expelled from the piston endof the left hand hydraulic cylinder assembly 122 through conduit 359and, at least one of the check valve 354 and the normally open, leftsecondary side shift control valve 348. Fluid returns to the reservoir306 through the side shift control valve 310 and the left hand clamp arm118 moves to the right in unison with the right hand clamp arm 116.

Conversely, moving the sideshift control valve 310 to the right from thecenter position directs fluid from the pump 304 into conduit 358. Thefluid flows through the normally open, left secondary side shift valve348 and into the piston end 330 of the left hand hydraulic cylinderassembly 122 through conduit 359. The left hand hydraulic cylinder isurged to extend and move the left hand clamp arm 118 left forcing fluidfrom the rod end 322 of the left hand hydraulic cylinder 122 throughconduit 352 to the rod end 324 of the right hand hydraulic cylinder 124.Fluid is expelled from the piston end of the right hand hydrauliccylinder assembly 124 through conduit 343 and, at least one of the checkvalve 356 and the normally open, left right secondary side shift controlvalve 346. Fluid returns to the reservoir 306 through the side shiftcontrol valve 310 and the right hand clamp arm 116 moves to the left inunison with the left hand clamp arm 118.

In addition, the exemplary attachment 102 includes a hydraulic motor 315arranged to rotate the attachment's load face about an axissubstantially parallel to the longitudinal centerline 134 of theforklift. The hydraulic motor 315 is controlled by a rotation controlvalve 314 similar to the side shift control valve 310 and theclamp/unclamp valve 312. Shifting the rotation control valve 314 in afirst direction directs oil into conduit 362 and through a normallyopen, secondary rotation control valve 364. Pressure in conduit 363unseats the pilot operated check valve 317 permitting fluid to flowthrough the check valve 319, the motor 315 and back to the reservoirthrough conduit 365 causing the motor to rotate the attachment's loadface in a first direction. Shifting the rotation control valve 314 inthe opposite direction from the center position causes the motor 315 torotate the attachment's load face in the direction opposite of the firstdirection.

The exemplary attachment 102 further comprises a side shift sensor(indicated generally as) 370 which may comprise multiple sensors asdescribed hereafter, a lift height sensor 372 and, preferably, a backtilt sensor 374. The lift height sensor 372 is preferably affixed to theframe 104 of the attachment 102 and enables determination of a distancebetween a height datum for the attachment, for example, the location ofthe lift height sensor, and the surface supporting the material handlingvehicle. Although the lift height may be measured directly, it may alsobe computed by sensing a distance to a reference datum on the materialhandling vehicle, for example the base of the mast 114, which has aknown or determinable distance from the ground. By way of examples only,the lift height sensor may comprise a laser range finder, a cableactuated encoder, an optical sensor arranged to detect targets affixedto the material handling vehicle or an accelerometer arranged todetermine displacement from a datum by dead reckoning.

The side shift sensor 370, which may comprise plural sensors 370A and370B, is preferably affixed to a portion of the attachment that does notmove laterally with respect to the material handling vehicle, such asthe frame 104 or the shells of the hydraulic cylinder assemblies 122,124, and enables determination of a distance between a lateral load facedatum, such as the lateral center 130 of the load face 133 as defined bythe load engaging members, and a lateral datum of the material handlingvehicle, such as the vehicle's longitudinal center line 134. Externalside shifting attachments comprise an actuator, typically a hydrauliccylinder assembly, which is dedicated to the side shift function,enabling the lateral displacement to be determined with a single sideshift sensor arranged to detect the displacement of the actuator oranother part of the attachment displaced by the actuator. On the otherhand, internal side shifting attachments, such as the exemplaryattachment 102, typically utilize plural actuators to provide forcoordinated movement of the clamp arms or other load engaging membersand the location of the load face lateral datum is, preferably,determined from respective measurements to each load engaging member116, 188 or a structural element movable with the load engaging membersby one or more side shift sensors, such as plural side shift sensors370A, 370B. The plural side shift sensors are preferably attached topoints fixed relative to the material handling vehicle, for examples theshells of the clamping/side shift hydraulic cylinder(s) as shown in FIG.2 or the attachment frame 104. By way of example only, the sideshiftsensor(s) 370 might comprise laser range finders, cable actuatedencoders, linear transducers, an accelerometer, optical sensors arrangedto detect and count or decode targets on movable portions of theattachment or the actuators as disclosed in U.S. Patent Publication No:US 2013/0277584 or one or more limit switches operable by lateraldisplacement of a portion of the attachment.

The exemplary attachment 102 also preferably, but not necessarily,includes a sensor 374 to detect the rearward tilt of the materialhandling vehicle's mast 114. The angle of the mast and load face of aforklift is typically changed by a pair of hydraulic tilt cylinderassemblies 720 connecting the forklift's frame and mast 114. Mast tiltmay be sensed, for example, by a linear transducer attached to the mastor one of the hydraulic tilt cylinder assemblies or, preferably, by aninclinometer or triaxial accelerometer affixed to the attachment.

Referring also to FIGS. 6A and 6B, an exemplary side shift limitingmethod 600 is executed by a controller 380, shown in FIG. 3, and,preferably, affixed to the attachment 102. The controller operatesaccording to instructions stored in a memory to periodically read theoutputs of the side shift sensor(s) at step 602, the lift height sensorat step 604 and, optionally, the back tilt sensor at step 606 and tooutput signals to activate transducers providing one or more alerts tothe operator of the material handling vehicle and/or limit the speedand/or displacement of the attachment if the sensed lateral displacementof a load face lateral datum exceeds one or more side shift limitscorresponding to the sensed lift height or, preferably, the sensed liftheight and back tilt. Referring also to FIG. 7, one or more side shiftlimits, for example side shift limits 702, 704, 706, may be stored in amemory of the controller 380 for each of plural lift heights, preferablyat one or more back tilt angles, or for each of plural values of arelationship combining back tilt and lift height. On the other hand, thecontroller may calculate one or more side shift limits for the sensedlift height or, alternatively, the sensed lift height and back tilt. Asillustrated in FIG. 7, the maximum side shift displacement 708, 710, oneither side of the fork lift center line datum 134 is preferablypermitted only at lower lift heights or when a relationship of liftheight and back tilt 712 is relatively low. By way of example only,“lower lift heights” might be lift heights lower than the mast'sfreelift height, i.e. the lift height at which the overall height of themast begins increasing, or a lift height enabling a second load to bedeposited on a load having the height of a rated load for the materialhanding vehicle. At higher lift heights, preferably combined with backtilt, side shifting displacement and speed may be restricted to limit orreduce the effects of lateral acceleration of an off-center load on thestability of the material handling vehicle. For example, unrestrictedside shift speed may be permitted within a first side shift limit 702and side shift displacement and attachment rotation, if applicable, and,optionally, hoisting and/or back tilting may be blocked at a maximumside shift limit 706 appropriate for a sensed a lift height and,preferably, a lift height and back tilt. At one or more other side shiftlimits between a first side shift limit 702 and a second side shiftlimit 706, for example side shift limit 704, other action may be takensuch as issuing various alerts to the operator and/or reducing the sideshift speed to reduce dynamic forces produced byacceleration/deceleration of the load and/or, if the attachment includesa rotator, blocking or limiting rotator speed. For example, the sideshifting speed may be restricted to vary proportionally ornon-proportionally with displacement over some portion of the side shiftdisplacement. Maximum side shift displacement may be permitted to aspecified lift height, and/or lift height and back tilt angle, and sideshift displacement may be restricted to a single value at greater liftheights or, as illustrated, there may be a range of lift heights or liftheight and back tilt angles where the permitted side shift displacementis changing according to a relationship with the lift height or,preferably, a relationship combining the lift height and the back tilt.Typically, the side shift limits are symmetrical about the longitudinalcenter line of the forklift but for certain loads the limits mightdiffer on respective sides of the centerline.

With reference to FIG. 6A, the controller 380 looks up, calculates orotherwise determines a first side shift limit at step 608, a firstlimiting value of the lateral displacement of a load face datum, forexample the center 130 of the load face 130 120, relative to a lateraldatum for the material handling vehicle, for example the longitudinalcenterline 134. For example the first side shift limit may be the valueof the side shift limit 702, corresponding to the sensed lift heightsensed at step 604 and preferably the sensed lift height sensed at step604 and back tilt sensed at step 606 measured by the respective sensors.At step 610, the controller compares the first right side shift limit tothe sensed side shift displacement. If the sensed side shiftdisplacement sensed at step 602 is not equal to or greater than thevalue of a first right hand side shift limit, the controller determinesif the side shift displacement is less than a first left side shiftlimit at step 612. In the example illustrated in FIG. 7 the magnitude ofthe right and left side shift limits are the same for any lift heightand back tilt but a position to the right of the lateral center 132 ofthe attachment's frame, and thereby to the right of the centerline 134of the forklift truck 100 (right side shift), may have a positive valuewhile a position to the left of the lateral center of the attachment(left side shift) may have a negative value. The lateral displacement ofthe load face datum 130 can be determined by, for example, subtractingfrom the lateral position of the right clamp arm 116 or adding to thelateral position of the left clamp arm 118 one half of the sum of theabsolute values of the lateral positions of the respective clamp arms,that is, one half of the distance 133 between the clamp arms 133 116,118. If the side shift displacement does not exceed either the firstright or first left side shift limit, the controller reads side shiftdisplacement sensed at step 602, the lift height sensed at step 604 and,preferably, the back tilt sensed at step 606 again.

If the sensed side shift displacement equals or exceeds one of the firstright or the first left side shift limit limits at steps 610, 612, thecontroller determines a second side shift limit at step 614 for therespective side shift direction. The second side shift limit, forexample, side shift limit 704, typically includes greater lateraldisplacement than the first side shift limit. The controller 380compares the sensed side shift displacement to the appropriate secondright 616 or left side shift limit limits at steps 616 and 618. If thesensed side shift exceeds a first side shift limit but does not equal orexceed the second right side shift limit at step 616 or the second leftside shift limit at step 618, as appropriate, the controller may signalat steps 620, 622 the appropriate one of the right secondary side shiftvalve 346 or the left secondary side shift valve 348 to restrict thefluid flowing in the appropriate direction to the side shift hydrauliccylinder(s) thereby the limiting the side shifting speed in thedirection that would tend to reduce the material handling vehicle'sresistance to tipping. Preferably, the right 346 and left 348 secondaryside shift valves and the secondary rotation valve 364 are proportionalflow valves arranged to meter the respective flows in response todiffering or varying signals, such as pulse width modulated signals,from the controller. Also preferably, the controller 380 includesinstructions to vary the signal to the secondary side shift valves andthe secondary rotation valve to variably restrict the respective flowsto control acceleration as well as the speed of the hydraulic actuatorslimiting forces produced by movement of the load.

If the side shift displacement exceeds the first side shift limit butdoes not exceed a second side shift limit, the controller 380 may signalan alert controller 386 to issue an operator alert at step 624. Theexemplary system 302 includes a first transducer 388 arranged tovisually alert the operator of the material handling vehicle that theside shift displacement has reached or is proximate a limit, and asecond transducer 390 to audibly alert the operator in response tosignals output by an alert controller 386. Preferably, the controller380 is located on the attachment and is communicatively connected to thealert controller 386 by a first radio frequency transceiver 382 and asecond radio transceiver 384 associated with the alert controller whichis preferably located on the material handling vehicle. The firsttransducer 388 may comprise, for example, an array of lights ofdifferent colors, a light which flashes at plural frequencies or adisplay for a text message to indicate that side shifting has reached oris proximate a side shift limit. The audible operator alertingtransducer 390 might, by way of example, comprise a tonal device whichannunciates a tone of varying frequency, amplitude or intermittence asthe side shift increases or the audible alert transducer may comprise aspeech synthesizer that emits recorded or synthesized messages, forexample advising the operator when the appropriate side shift limit isreached or is approaching, that further side shifting will be slowed orblocked and/or that the attachment should be centered, if possible. Ifthe side shift displacement exceeds either of the first side shiftlimits but not the second side shift limit, the controller 380 reads thelift height at step 604, back tilt at step 606 and side shift at step602 sensors again.

Referring also to FIG. 6B, if, however, the side shift displacementexceeds the first and the second side shift limit, the controllerdetermines a next side shift limit and repeats the process until thesensed side shift displacement no longer exceeds a side shift limit. Forexample, in a system with n side shift limits, if the sensed side shiftexceeds the first n−2 side shift limits but does not exceed the rightn−1 side shift limit at step 638 or the left n−1 side shift limit atstep 640, for example, the controller 380 may signal the appropriatesecondary side shift valve to further reduce the side shift speed atsteps 642, 644 and direct the alert controller 386 to issue a differentoperator alert at step 646. If the attachment includes a rotator, thecontroller may signal the secondary rotation control valve 364 torestrict or prevent rotation at step 648 to prevent or lessen dynamicforces accompanying a change in speed or position of the load's centerof mass.

If the side shift displacement exceeds either the right or the left n−1(next to last) side shift limit, the controller 380 determines at step650 the maximum side shift limit (limit n), for example limit 706,corresponding to the sensed lift height and, preferably, back tilt, 650.The controller compares the sensed side shift displacement to theappropriate right 652 or left 654 maximum side shift limit at step 652and the appropriate left maximum side shift limit at step 654. If thesensed side shift displacement does not equal or exceed one of themaximum side shift limits, the controller 380 may further restrict theappropriate right 656 or left 658 side shift speed at step 656 and theappropriate left side shift speed at step 658, issue a new operatoralert or continue the issuance of an earlier operator alert at step 660and block or continue to block rotation at step 662.

If, however, the side shift displacement equals or exceeds one of theright 652 or left 654 maximum (n) side shift limits at the sensed liftheight and, preferably back tilt, the controller preferably signals theappropriate secondary side shift valve 346, 348 to block further sideshift displacement in the direction of the maximum limit at steps 664,and 666, respectively. In addition, the controller 380 may signal thealert controller 386 to issue another operator alert at step 668, blockrotation at step 670 and block lifting and/or back tilting at step 672.The check valves 354, 356 permit fluid to flow from the respectivepiston ends 330, 332 of the hydraulic cylinders 122, 124 enablingcentering of the attachment even if the right secondary side valve 346or the left secondary side shift valve 348 is shifted to block a flow offluid which would increase the side shifting. In any event, thecontroller 380 continues sampling the output of the side shift, liftheight and back tilt transducers and comparing the sensed side shiftdisplacement to one or more side shift limits for the sensed lift heightand preferably the sensed lift height and sensed back tilt.

Alternatively, the controller 380 may transmit signals to the alertcontroller 386 to control the side shifting and rotation of theattachment and, optionally, the lifting and/or tilting of the materialhandling vehicle's mast. If the material handling vehicle is equippedwith a remotely controllable side shift valve, such as side shift valve310, the side shift displacement and speed may be controlled byoperation of the side shift valve without intervention of secondary sideshift valves, such as secondary side shift valves 346, 348. Instructionsfrom the controller 380 and, preferably, relayed by the alert controller386 to a vehicle controller 710 711 which controls the operation of aremotely operable side shift valve 310 may cause the vehicle controllerto manipulate the remotely operable side shift valve to change the sideshift speed and maximum lateral displacement or to cause the attachmentto be displaced toward the center of the frame as the lift height and/orback tilt increases to keep the side shift within a limit. On the otherhand, the alert controller could be arranged to transmit a signaldirectly to a remotely operable valve, such as tilt valve 716, to causethe valve to control the operation of associated transducers, such astilt cylinders 720.

Optionally, functions such as lifting and tilting may be controlled withsecondary valves, such as the secondary lifting control valve 714 andthe secondary tilting control valve 722. If the operator of the materialhandling vehicle attempts to lift a side shifted load to a height thatwould exceed an allowable lift height for the sensed lateral position ofthe load, a signal from the controller 380 or the alert controller 386can shift a secondary lifting valve 714 to block the flow of hydraulicfluid from the material handling vehicle's hoist valve 712 713preventing further lifting. Likewise, if the operator of the materialhandling vehicle attempts to tilt the vehicle's mast at a lift heightthat would exceed an allowable lift height and back tilt for the sensedlateral position of the load, a signal from the controller 380 or thealert controller 386 can shift a secondary tilting control valve 722 tolimit or block the flow of hydraulic fluid from the material handlingvehicle's tilt control valve 716 limiting the speed or preventingfurther back tilting.

The side shift limiting attachment alerts the operator if lateraldisplacement of the load face is approaching a limit for a lift heightand, preferably, back tilt and blocks or slows further side shiftingand/or rotation of the attachment when a side shift limit is reached fora specific lift height and back tilt.

The detailed description, above, sets forth numerous specific details toprovide a thorough understanding of the present invention. However,those skilled in the art will appreciate that the present invention maybe practiced without these specific details. In other instances, wellknown methods, procedures, components, and circuitry have not beendescribed in detail to avoid obscuring the present invention.

All the references cited herein are incorporated by reference.

The terms and expressions that have been employed in the foregoingspecification are used as terms of description and not of limitation,and there is no intention, in the use of such terms and expressions, ofexcluding equivalents of the features shown and described or portionsthereof, it being recognized that the scope of the invention is definedand limited only by the claims that follow.

We claim:
 1. A system for limiting a lateral position of a load face forand associated with a material handling vehicle, the system comprising:(a) a lateral position sensor arranged to output a lateral positiondatum quantifying representative of a distance between a materialhandling vehicle lateral datum longitudinal centerline and a load facelateral datum; (b) a height sensor arranged to output a height datumquantifying representative of a height of a vertical the load face datumrelative to a surface supporting said material handling vehicle; and (c)a controller arranged to receive said lateral position datum and saidheight datum and to output a first side shift control signal when saidlateral position datum corresponds to a first side shift limit for atsaid height datum and output a second side shift control signal whensaid lateral position datum corresponds to a second side shift limit atsaid height datum, the first side shift limit having a magnitude greaterthan that of the second side shift limit relative to the longitudinalcenterline, and each of the first and second side shift control signalsrestricting the lateral motion of the load face.
 2. The system forlimiting a lateral position of a load face for a material handlingvehicle of claim 1 further comprising a tilt sensor arranged to output atilt datum quantifying an angle of said load face, said controllerarranged to receive said tilt datum and output said side shift controlsignal when said lateral position datum corresponds to a side shiftlimit for said height datum and said tilt datum.
 3. The system forlimiting a lateral position of a load face for a material handlingvehicle of claim 1 further comprising a side shift indicator responsiveto at least one of said first side shift control signal and said secondside shift control signal to announce that said load face lateral datumcorresponds to the respectively associated said side shift limit.
 4. Thesystem for limiting a lateral position of a load face for a materialhandling vehicle of claim 3 wherein announcement that said load facelateral datum corresponds to said side shift limit the side shiftindicator comprises an optical signal.
 5. The system for limiting alateral position of a load face for a material handling vehicle of claim3 wherein announcement that said load face lateral datum corresponds tosaid side shift limit the side shift indicator comprises an audiblesignal.
 6. The system for limiting a lateral position of a load face fora material handling vehicle of claim 3 further comprising a second sideshift indicator responsive to a second side shift control signal outputby said controller to announce that said load face lateral datum isproximate at least one of said first side shift limit and said secondside shift limit.
 7. The system for limiting a lateral position of aload face for a material handling vehicle of claim 6 whereinannouncement that said load face lateral datum corresponds to said sideshift limit said side shift indicator comprises a first optical signaland said announcement that said load face lateral datum is proximatesaid side shift limit second side shift indictor comprises a secondoptical signal.
 8. The system for limiting a lateral position of a loadface for a material handling vehicle of claim 6 wherein announcementthat said load face lateral datum corresponds to said side shift limitsaid side shift indicator comprises a first audible signal and saidannouncement that said load face lateral datum is proximate said sideshift limit second side shift indicator comprises a second audiblesignal.
 9. The system for limiting a lateral position of a load face fora material handling vehicle of claim 1 further comprising a side shiftcontrol responsive to where said first side shift control signal torestrict restricts a speed of lateral movement of said load face whensaid lateral position datum corresponds to said first side shift limit.10. The system for limiting a lateral position of a load face for amaterial handling vehicle of claim 1 9wherein said side shift controlresponsive to said second side shift control signal blocks lateralmovement of said load face when said lateral position datum correspondsto said side shift limit.
 11. The system for limiting a lateral positionof a load face for a material handling vehicle of claim 9 furthercomprising a side shift indicator responsive to said first side shiftcontrol signal to announce that said load face lateral datum correspondsto said first side shift limit.
 12. The system for limiting a lateralposition of a load face for a material handling vehicle of claim 11wherein announcement that said load face lateral datum corresponds tosaid side shift limit said side shift indicator comprises an opticalsignal.
 13. The system for limiting a lateral position of a load facefor a material handling vehicle of claim 11 wherein announcement thatsaid load face lateral datum corresponds to said side shift limit saidside shift indicator comprises an audible signal.
 14. The system forlimiting a lateral position of a load face for a material handlingvehicle of claim 11 further comprising a second side shift indicatorresponsive to a the second side shift control signal output by saidcontroller to announce that said load face lateral datum is proximatesaid second side shift limit.
 15. The system for limiting a lateralposition of a load face for a material handling vehicle of claim 14wherein announcement that said load face lateral datum corresponds tosaid side shift limit said side shift indicator comprises a firstoptical signal and said announcement that said load face lateral datumis proximate said side shift limit second side shift indicator comprisesa second optical signal.
 16. The system for limiting a lateral positionof a load face for a material handling vehicle of claim 14 whereinannouncement that said load face lateral datum corresponds to said sideshift limit said side shift indicator comprises a first audible signaland said announcement that said load face lateral datum is proximatesaid side shift limit second side shift indicator comprises a secondaudible signal.
 17. The system for limiting a lateral position of a loadface for a material handling vehicle of claim 9 wherein said side shiftcontrol permits permitting lateral movement of said load face todecrease a distance between said material handling vehicle lateral datumlongitudinal centerline and said load face lateral datum when saidlateral position datum corresponds to at least one of said first sideshift limit and said second side shift limit.
 18. The system forlimiting a lateral position of a load face for a material handlingvehicle of claim 9 further comprising a rotator control responsive tosaid side shift control signal to interrupt rotation of said load facewhen said lateral position datum corresponds to at least one of saidfirst side shift limit and said second side shift limit.
 19. The systemfor limiting a lateral position of a load face for a material handlingvehicle of claim 1 further comprising a lifting control responsive tosaid side shift control signal to prevent increasing said height datumwhen said lateral position datum corresponds to said side shift limit.20. The system for limiting a lateral position of a load face for amaterial handling vehicle of claim 2 further comprising a tiltingcontrol responsive to said side shift control signal to prevent anincrease in said tilt datum when said lateral position datum correspondsto said side shift limit.
 21. A load handling attachment for a materialhandling vehicle, said load handling attachment comprising; (a) a loadface defined by a load engaging member and movable laterally andvertically relative to said material handling vehicle; (b) a lateralposition sensor arranged to output a lateral position datum quantifyingrepresentative of a distance to a lateral load face datum from areference position; (c) a height sensor arranged to output a heightdatum quantifying representative of a distance between a load faceheight datum and a surface supporting said material handing vehicle; and(d) a controller arranged to receive said lateral position datum andsaid height datum and operable according to a stored instruction tooutput a first side shift control signal when said lateral positiondatum exceeds a first side shift limit for at said height datum andselectively output a second side shift control signal when said lateralposition datum exceeds a second side shift limit at said height datum,the second side shift limit different in magnitude from that of thefirst side shift limit, each of the first and second side shift controlsignals restricting the lateral motion of the load face.
 22. The loadhandling attachment of claim 21 further comprising a side shift controldevice to limit a speed of lateral displacement of said lateral loadface datum in response to said first side shift control signal.
 23. Theload handling attachment of claim 22 wherein said side shift controldevice prevents a lateral displacement of said lateral load face datumin response to said second side shift control signal.
 24. The loadhandling attachment of claim 23 wherein said side shift control devicepermits decreasing said lateral displacement of said lateral load facedatum when increasing said lateral displacement is blocked.
 25. The loadhanding attachment of claim 21 further comprising a tilt sensor arrangedto quantify an angular orientation of said load face, said controllerarranged and operable according to a stored instruction to output said arespective one of the first side shift control signal and the secondside shift control signal when said lateral position datum exceeds aside shift limit for said height datum at a predetermined angularorientation.
 26. The load handling attachment of claim 21 furthercomprising: (a) an actuator arranged to selectively rotate said loadface; and (b) a rotation control arranged to limit a speed of rotationof said load face in response to at least one of said first side shiftcontrol signal and a rotation control signal from said controller andsaid second side shift control signal.
 27. The load handling attachmentof claim 21 further comprising an audible side shift indicatorresponsive to said side shift control signal to audibly annunciate thatsaid lateral displacement of said load face is proximate a side shiftlimit.
 28. The load handling attachment of claim 21 further comprising avisual side shift indicator responsive to said side shift control signalto visually signal that said lateral displacement of said load face isproximate a side shift limit.
 29. The load handling attachment of claim21 further comprising a lifting control device responsive to said sideshift control signal to prevent an increase in said height datum whensaid lateral position datum exceeds a side shift limit for said heightdatum.
 30. The load handling attachment of claim 25 further comprising atilting control device responsive to said side shift control signal toprevent a change in said angular orientation of said load face when saidlateral position datum exceeds a side shift limit.
 31. A method forlimiting a lateral position of a load face for a material handlingvehicle, the method comprising the steps of: (a) quantifying a distancebetween a material handling vehicle lateral datum and a load facelateral datum; (b) quantifying a height of a vertical load face datumrelative to a surface supporting said material handling vehicle; and (c)limiting a the speed of at which lateral displacement of said load facedatum when occurs whenever said distance between said material handlingvehicle lateral datum and said load face lateral datum corresponds toexceeds a limit at said height datum.
 32. The method of limiting thelateral position of a load face for a material handling vehicle of claim31 further comprising the steps of: (a) quantifying an angle of saidload face; and (b) further limiting said speed of lateral displacementwhen said distance between said material handling vehicle lateral datumand said load face lateral datum corresponds to a limit at said heightdatum and said angle of said load face.
 33. The method of limiting thelateral position of a load face for a material handling vehicle of claim31 further comprising the step of displaying an optical signal when saiddistance between said material handling vehicle lateral datum and saidload face lateral datum is proximate said limit.
 34. The method oflimiting the lateral position of a load face for a material handlingvehicle of claim 31 further comprising the step of annunciating anaudible signal when said when said distance between said materialhandling vehicle lateral datum and said load face lateral datum isproximate said limit.
 35. The method of limiting the lateral position ofa load face for a material handling vehicle of claim 31 furthercomprising the step of preventing an increase in said height of saidvertical load face datum when said distance between said materialhandling vehicle lateral datum and said load face lateral datumcorresponds to said limit.
 36. The method of limiting the lateralposition of a load face for a material handling vehicle of claim 31further comprising the steps of: (a) quantifying an angle of said loadface; and (b) preventing an increase in said angle of said load facewhen said distance between said material handling vehicle lateral datumand said load face lateral datum corresponds to said limit.
 37. Thesystem of claim 1 where the first side shift limit and the second sideshift limit at said height datum are each predetermined prior to a timethat the material handling vehicle engages a load.
 38. The load handlingattachment of claim 21 where the first side shift limit and the secondside shift limit at said height datum are each predetermined prior to atime that the load handling attachment engages a load.
 39. The method ofclaim 31 where the limit at said height datum is predetermined prior toa time that the material handling vehicle engages a load.